This invention is directed generally to fluid warming apparatus and, more particularly, to a monitoring circuit for use in apparatus for warming parenteral fluids such as whole blood for intravenous injection or transfusion procedures.
Whole blood is commonly stored in blood banks at a reduced temperature in the order of 4.degree. C. To prepare this blood for infusion into a patient, it is necessary that the blood be warmed to the temperature of the human body, which is nominally 37.degree. C. For applications where substantial and unpedictable quantities of blood may be required, such as where a patient hemorrhages during surgery, it is preferable that the blood be transferred from storage directly to the patient, since this avoids warming blood which is not subsequently used.
One effective and efficient apparatus for dry warming blood or other parenteral fluids to body temperature during the process of infusing such fluids into the patient is described in the copending application of Baxter Travenol Laboratories, Inc., Ser. No. 761,926, filed Jan. 24, 1977. It is a feature of this apparatus that the temperature of the infused blood is maintained constant at 37.degree. C. substantially independently of flow rates, which may vary from 0 tp 150 ml per minute depending on the needs of the patient. Sterility of the blood is maintained and contamination of the apparatus is avoided by use of a disposable flow system having a blood warming bag which fits within the apparatus in thermal communication with electric heating elements.
The present invention is directed to a monitoring circuit which, when incorporated in the apparatus, provides both a digital indication of blood temperature and constant protection against overtemperature operation independent of the control circuitry of the apparatus. By reason of its novel construction, the monitoring circuit is incorporated in the apparatus with minimal changes to existing circuitry.
Accordingly, it is a general object of the present invention to provide new and improved apparatus for warming blood and other parenteral fluids prior to infusion into the human body.
It is another object of the present invention to provide a new and improved monitoring circuit for apparatus for warming blood and other parenteral fluids prior to infusion into the human body.
It is another object of the present invention to provide a new and improved monitoring circuit for a blood warming apparatus which provides improved protection against malfunction of the apparatus.
It is another object of the present invention to provide a new and improved blood warming apparatus which provides a digital temperature readout of improved accuracy.